Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover. It is also possible to surround a hollow or fluid-filled center with a plurality of solid layers. Solid balls have traditionally been considered longer and more durable than wound balls, but many solid constructions lack the “feel” provided by the wound construction.
More recently, by altering solid golf ball construction and composition, manufacturers have been able to vary a wide range of playing characteristics, such as compression, velocity, “feel,” and spin, optimizing each or all as needed. In particular, a variety of core and cover layer constructions, such as multi-layer golf balls having dual cover layers and/or dual core layers, have been investigated and now allow many non-wound balls to exhibit characteristics previously unattainable in a solid-construction golf ball. These golf ball layers are typically constructed with a number of polymeric compositions and blends, including polybutadiene rubber, thermoplastic and thermoset materials, polyurethanes, polyamides, and ethylene-based ionomers.
The core of solid golf balls is the “engine” of the ball, providing the velocity required for good distance. Too hard a core, however, can result in a golf ball that provides poor “feel,” particularly apparent when hit by an accomplished golfer. Manufacturers are constantly experimenting with various core compositions and constructions in an effort to optimize both feel and distance. Most conventional solid cores comprise polybutadiene rubber or some modified form thereof. For example, polybutadiene has a number of isomers (i.e., cis-, trans-, and vinyl-) or may contain a variety of filler materials (i.e., ZnO, W, or microspheres). When fillers, such as tungsten, are included, they are generally combined with the polybutadiene master batch just prior to the molding step. The result is a plethora of tungsten dust, an obvious hazard that also clogs golf ball molds and is difficult to clean.
It has been determined that, by adding tungsten (or other filler) to a second batch of polybutadiene rubber in concentrated amounts and subsequently blending the second batch, in a predetermined amount, with the master batch, tungsten can be added to the master batch in a non-hazardous manner.